Just saw your NEW POST -- if the Vizio remote does control the volume, and the Cable remote does not....reinstall your TV code on the Cable remote. It's either corrupted and needs re-installed or the Cable remote has failed.
Never mind the info below. I just pressed the Information Request button and saw your response at that time.
You probably have the Touchpad buttons and that's why you can't find it. The first time I ran across them, I was saying "where's the buttons at? Don't tell me the manufacturer decided to not install them." Then my customer "stroked" the plastic frame by the power button and they lit up.
"Oh.....that's new. They sure didn't mention that in training".
Anyways, issues like you experience, we always reset the TV and/or cable box FIRST. The reason is simply because software can get corrupted on TVs just as much as it can lock up a computer. And the only way to reload software on a TV or cable box is to unplug it for 5 minutes.
We really want to make sure the software isn't corrupted. If your TV's volume control doesn't work after the reset, we do want to check the "well hidden" front panel controls to see if they work or not. The remote control has it's own computer too, and it can lock up and produce the no volume control issue too.
Unplug the battery on that, but only for a minute. Press the power button on the remote to drain the power off of the computer.
If it still fails afterwards....then we start looking at hardware failures instead of software failures.